Travelling-wave tube having integrated tuning plunger to impedance match too-short internal coupling to external circuitry



ER TO Dec. 13, 1966 RYUZO ORUI TRAVELLING-WAVE TUBE HAVING INTEGRATED TUNING PLUNG IMPEDANCE MATCH TOO-SHORT INTERNAL COUPLING TO EXTERNAL GIRCUITRY Filed March 26, 1963 2 Sheets-Sheet 1 km? QQkxQ kt? mxQkxl m Y m T N WN mi N N\ \Q B m MM W I :IIrC Z Y A J /fi/ \N E II I mm mm Ev mail U Q T@ RoRui Attorney 1966 RYUZO ORUI 3,292,032

TRAVELLING-WAVE TUBE HAVING INTEGRATED TUNING PLUNGER To IMPEDANCE MATCH TOO-SHORT INTERNAL COUPLING TO EXTERNAL CIRGUITRY Filed March 26, 1963 2 Sheets-Sheet 2 m m w w Q 1 R ww w Q w R H @w I v wwi TIU Q Q v nwt M I/ 3, 1Q /////m/v w/ /W,V- 4///\/ Qw ww @w Nw m \w Attorney llnitcd States Patent TRAVELLING-WAVE TUBE HAVING INTE- GRATED TUNING PLUNGER T0 IMPED- ANCE MATCH. TOO-SHORT INTERNAL COUPLING T0 EXTERNAL CIRCUITRY Ryuzo Orui, Tokyo, Japan, assignor to Nippon Electric *"CompanyyLimited, Tokyo, Japan, a corporation of Ja an Filed Mar. 26, 1963, Ser. No. 268,058 Claims priority, application Japan, Sept. 18, 1962, p 37/ 40,474

f3 Claims. (Cl. 315-35) "I This invention relates to a coupling device for electromagnetically coupling the electrode forming a slow-wave structure of a travelling wave tube with an external highfrequency circuit.

- In general, a travelling wave tube is mounted on a radio communication apparatus in either of the following ways: one method is to put a travelling wave tube into a radio communication apparatus already provided with a'magnetic focussing device and a coupling for the travelling wave tube and another method is to provide a radio communication apparatus with only a magnetic focussing device and to provide an integral assembly of a travelling wave tube and a coupling waveguide therefor.

Withv the former method, it is necessary after instalation 'of the travelling wave tube, to efiect impedance matching or to adjust the high-frequency coupling between the coupling waveguide and the travelling wave tube. This method has disadvantages in that such adjustment must be completed at the location of the radio communication apparatus requiring provision of particular measuring equipments at this location. Also, the method is inconvenient because the adjustment must be performed each time the travelling wave tube is replaced to overcome the mismatch caused by variations in dimensions of the travelling wave tubes.

With the latter method, it is possible to avoid the difficulties of the former method because perfect matching between the travelling wave tube and the coupling waveguide during manufacture, completely dispels the necessity of on-the-spot adjustment and facilitates replacement of the travelling wave tube. However in past tube assemblies the added couplings have resulted in bulky components.

It is an object of this invention to provide an assembly of a tube and coupled waveguide which occupies less total space than prior structures.

The arrangement for the latter method as well as the invention itself will be explained with reference to the accompanying drawing, in which:

FIG. 1 is a longitudinal sectional view of a conventional coupling device for a travelling wave tube;

FIG. 1(a) is a cross-sectional view on line a-a' of FIG. I viewed from the lefthand side;

FIG. 1(b) is another cross-sectional view on line b-b of FIG. I viewed from righthand side;

FIG. 2 is a longitudinal sectional view of an embodiment of the coupling device for a slow-wave structure according to the invention;

FIG. 2(a) is a cross-sectional view on line a-a' of FIG. 2 viewed from the lefthand side; and

FIG. 2(b) is another cross-sectional view on line b-b' of FIG. 2 viewed from righthand side.

Now a conventional arrangement of an assembly ac cording to the above-mentioned latter method will first be explained with reference to FIGS. 1, 1(a), and 1(b). A travelling wave tube 1 has, within a vacuum envelope 2, an electron gun 3, an input-side choke member 4, an input antenna 5, a helical slow-wave structure 6, an output-side choke member 7, an output antenna 8, and a collector 9.

3,292,032 Patented Dec. 13, 1966 Input coupling waveguide 11 and an output coupling Waveguide 21 are both shown as rectangular for propagation of an H Wave in the axial direction of the travelling Wave tube 1 and adapted for transferring the hightrequency power to and from a radio communication apparatus. The input and the output coupling waveguides 11 and 21 have longitudinal portions .12 and 22, transverse portions v13 and 23 provided with holes 14 and 24Afor receiving the travelling-wave tube 1, cylindrical portions 15 and 25 covering the choke members 4 and 7, and short-circuiting walls 16 and 26, respectively. The travelling wave tube 1 and the input and the output coupling waveguides 11 and 21 are supported within a non-magnetic metal envelope 31.

The detailed operation of the coupling device of FIG. 1 will not be explained here because it is not only similar to that of the widely used coupling device between a helical slow-wave structure and waveguides but also described in my copendin-g patent application, Serial No. 243,900, filed Dec. 11, 196 2. It is, however, to be noted that for best results the distance betwen the antenna 5 or 8 and the short-ci-rcuiting wall .16 or 26 must be about a quarter wavelength of the electromagnetic wave being handled. A disadvantage of the coupling device of FIG. 1 is the unavoidably large diameter of the metal envelope 31 due to disposition of the rectilinear portion 12 of the input coupling waveguide 11 beyond the short-circuiting wall 26 of the output coupling waveguide 21. Consequently the coupling device shown in FIG. \1 has a large volume and requires a large diameter magnetic cfooussing device installed in the radio communication apparatus adding considerable bulk to the radio communication apparatus.

This invention removes such defects of the conventional coupling device and provides a coupling device for a slow-wave structure wherein the diameter of the metal envelope is relatively small.

Now the invention will be explained with reference to FIG. 2 which shows an embodiment of the invention.

The coupling device shown in FIG. 2 reduces the dimensions of the device of FIG. 1 by a variation in the output couplin waveguide. This output coupling waveguide 41 comprises longitudinal portions 42 and 43 extending axially of the travelling-wave tube, an E-branch waveguide 44 extending from the junction of rectilinear portions 42 and 43 transversely of the axis of the travelling wave tube provided with a hole 45 for passage of the travelling wave tube, a metal tube 46 covering the output-side choke member 7, a short-circuiting wall 47 at the end of the E-branch waveguide, and an adjustable short-circuiting member 48 disposed within the rectilinear portion 43.

As the distance between the output antenna 8 and the short-cirouiting wall 47 is made considerably shorter than a quarter of the guide wavelength with a view to reducing the outer diameter of the metal envelope 31, mismatching would result and a standing wave would appear in the E-branch waveguide 44 if only this change were made. The circuit consisting of the rectilinear portion 43 with the adjustable short-circuiting member 48 gives a series reactance to the rectilinear portion 42 at a branch point 49 of the E-branch waveguide 44. The reactance is a function of the distance between the junction 49 and the adjustable short-circuiting member 48 and assumes an optional value between zero and positive or negative infinity. Therefore, by adjusting of the short-circuiting member 48 the series reactance given at the junction 49 by the circuit consisting of the rectilinear portion 43 and the adjustable short-circuiting member 48, the reactance component of the impedance of the otherwise mismatched E-branch waveguide 44 seen from the junction 49 is cancelled and the appearance of the standing Wave in rectilinear portion 42 is avoided.

While the single embodiment has been used to explain the invention, it is to be understood that modifications are possible within the scope of the invention, such as, to substitute a sector or otherwise modified waveguide for the rectangular waveguide.

Furthermore, it is to be noticed that the words travelling wave tube and slow-Wave structure are used in their broadest sense.

What is claimed is:

1. In a travelling wave tube assembly having a slowwave structure extending linearly between input and output coupling devices within an evelope, an input waveguide and an output waveguide positioned diametrically with respect to said envelope and extending substantially parallel to said slow-Wave structure from the output end thereof;

each waveguide having a connected waveguide portion aligned transverse to said slow-wave structure and embracing and extending beyond their respective input and output coupling devices;

the input transverse waveguide portion extending beyond its associated coupling device;

said output transverse section extending beyond its associated coupling device;

a further waveguide portion connected to said output waveguide and extending linearly beyond the juncthe 3. In a travelling wave tube assembly having a slowtion of said output Waveguide and its associated transverse waveguide portion; said further waveguide portion having an impedance to compensate for the shorter length of the extended transverse waveguide portion. 2. The assembly of claim 1 being mounted within an external housing.

put coupling devices within an envelope, an input waveguide and an output waveguide positioned diametrically with respect to said envelope and extending parallel to said slow-wave structure from the output end thereof, each waveguide having a connected waveguide portion aligned transverse to said slow-wave structure and embracing and extending beyond the respective input and output coupling devices, the input transverse waveguide portion extending substantially a quarter of a guide wavelength beyond the associated coupling device, said assembly being mounted within an external housing, an arrangement permitting said housing to have a reduced diameter comprising said output transverse section being extended a distance less than a quarter wavelength beyond its associated coupling device, said input waveguide having a surface substantially contiguous with the end of said last-named extended'transverse waveguide portion, a further waveguide portion connected to said out: put Waveguide and extending longitudinally beyond the junction of said output waveguide and the said associated transverse waveguide portion, and'an adjustable shortcircuiting device within said further waveguide portion to adjust its impedance to compensate for the shorter length of the extended transverse waveguide portion.

References Cited bythe Examiner UNITED STATES PATENTS 2,580,007 12/1951 Dohler et al. 315-39 2,850,704 9/1958 Munushian 315-3.5 X

ELI LIEBERMAN, Primary Examiner.

R. D. COHN, Assistant Examiner. 

1. IN A TRAVELLING WAVE TUBE ASSEMBLY HAVING A SLOWWAVE STRUCTURE EXTENDING LINEARLY BETWEEN INPUT AND OUTPUT COUPLING DEVICES WITHIN AN EVELOPE, AN INPUT WAVEGUIDE AND AN OUTPUT WAVEGUIDE POSITIONED DIAMETRICALLY WITH RESPECT TO SAID ENVELOPE AND EXTENDING SUBSTANTIALLY PARALLEL TO SAID SLOW-WAVE STRUCTURE FROM THE OUTPUT END THEREOF; EACH WAVEGUIDE HAVING A CONNECTED WAVEGUIDE PORTION ALIGNED TRANSVERSE TO SAID SLOW-WAVE STRUCTURE AND EMBRACING AND EXTENDING BEYOND THEIR RESPECTIVE INPUT AND OUTPUT COUPLING DEVICES; THE INPUT TRANSVERSE WAVEGUIDE PORTION EXTENDING BEYOND ITS ASSOCIATED COUPLING DEVICE; SAID OUTPUT TRANSVERSE SECTION EXTENDING BEYOND ITS ASSOCIATED COUPLING DEVICE; A FURTHER WAVEGUIDE PORTION CONNECTED TO SAID OUTPUT WAVEGUIDE AND EXTENDING LINEARLY BEYOND THE JUNCTION OF SAID OUTPUT WAVEGUIDE AND ITS ASSOCIATED TRANSVERSE WAVEGUIDE PORTION; SAID FURTHER WAVEGUIDE PORTION HAVING AN IMPEDANCE TO COMPENSATE FOR THE SHORTER LENGTH OF THE EXTENDED TRANSVERSE WAVEGUIDE PORTION. 